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What: Push some ob1 optimizations to the trunk and 1.7.5.
What: This patch contains two optimizations:
- Introduce a fast send path for blocking send calls. This path uses
the btl sendi function to put the data on the wire without the need
for setting up a send request. In the case of btl/vader this can
also avoid allocating/initializing a new fragment. With btl/vader
this optimization improves small message latency by 50-200ns in
ping-pong type benchmarks. Larger messages may take a small hit in
the range of 10-20ns.
- Use a stack-allocated receive request for blocking recieves. This
optimization saves the extra instructions associated with accessing
the receive request free list. I was able to get another 50-200ns
improvement in the small-message ping-pong with this optimization. I
see no hit for larger messages.
When: These changes touch the critical path in ob1 and are targeted for
1.7.5. As such I will set a moderately long timeout. Timeout set for
next Friday (Jan 17).
Some results from osu_latency on haswell:
hjelmn_at_cn143 pt2pt]$ mpirun -n 2 --bind-to core -mca btl vader,self ./osu_latency
# OSU MPI Latency Test v4.0.1
# Size Latency (us)
- application/pgp-signature attachment: stored